Polymerization process involving three monomers



Sept. 9, 1958 G. L. wEsP ETAL POLYMERIZATION RROCSS INVOLVING THREE MONOMERS Filed DSG. 7. 1953 2 Sheets-Sheet 1 ALJ NVV

, Nv MA W/VV, /VWM sept 9 1958 G. L. wEsP ErAL 2,851,447

` PoLYMERIzATIoN PRocEss INvoLvING THREE MoNoMERs Filed no. 7; 195s z sheets-sheet 2 NAVA VWA v mv i Bylc*United States Patent G PLYMERIZATION PROCESS INVOLVING THREE MUNOMERS George L. Wesp, Englewood, and Robert Slocornbe,

Dayton, Uhio, assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware Application December 7, 1953, Serial No. 396,485 ,i

17 Claims. (Cl. Zoll-80.5)

This invention relates to three-component interpolymers, commonly called terpolymers, i. e., interpolymers prepared by polymerizing a monomeric mixture consisting of three different monomers. In specific aspects the invention pertains to terpolymers of (a) ocmethylstyrene, (b) acrylonitrile, and (c) a monomer selected from the group consisting of methacrylonitrile and alkyl methacrylates. Other aspects of the invention relate to improved -methods of preparing clear terpolymers.

It is by now well known that ethylenically unsaturated monomers differ greatly in their polymerization reactivity toward each other. There are in fact some monomers, including -methylstyrene in free-radical-initiated systems, that will not undergo homopolymerization at all, i. e., polymerization of two or more molecules of the same monomer to form a polymer of that monomer, yet will readily undergo interpolymerization with certain other monomers. Interpolymerization affords a method of imparting varying characteristics to a polymer, and in many instances such characteristics cannot be obtained by mere physical admixture of two or more homopolymers. However, because of the above-mentioned differences in reactivity among monomers toward each other, marked heterogeneity is the rule in interpolymers and only under special circumstances can an interpolymer be obtained that is of sucient homogeneity to give a transparent or clear interpolymer. While some objectionable properties such as color, encountered. in interpolymers, can often be avoided by means such as the use of stabilizers or lower polymerization temperatures, incompatibility manifested by haze, turbidity or opacity in plastics is not overcome by such treatment.

If a monomeric mixture is subjected to polymerization and the initial increment of polymer is segregated before the polymerization is allowed to go forward to an appreciable extent, it is frequently possible to obtain a clear interpolymer, but the commercial impracticability of such a procedure is apparent. On the other hand, if polymerization is permitted to proceed to a considerable and especially to a high degree of conversion, the more reactive monomer enters into the polymer to a greater extent than a less reactive monomer or monomers with the consequence that residual unreacted monomer becomes more and more depleted in the more reactive monomer, while the polymer being formed in the latter stages of polymerization is deficient in the more reactive monomer. There results a polymeric material which is made up of a variety of polymer molecules running a gamut of compositions such that the total polymer is heterogeneous with resultant opacity and often greatly impaired physical properties. This phenomenon, resulting in an undesirable product, can be overcome to an appreciable but limited extent by gradually adding during the course of the polymerization the more reactive monomer at a rate aimed at keeping the composition of unreacted monomeric mixture essentially constant. As a practical matter it is extremely dicult to approach uniformity in such an operation, and it is impossibleto use this technique at all in the case of mass (bulk) polymerization in which the polymerization reaction mixture sets up into semi-solid or solid polymer after the reaction is only partly completed so that further access of added monomer to the total mixture cannot be obtained.

lt is only in recent years that systematic laboratory and theoretical studies of interpolymerization have gone forward suciently to permit a certain amount of predictability in this eld. It has been theorized that in a simple binary system involving the free-radial-initiated polymerization of only two monomers, the composition of polymer will be dependent only upon the rate of four propagation steps, i. e., steps in the propagation of polymer molecules.

Growing Adding Rate of Process Reaction Chain Monomer Product 'w' mr M1 krimi-HMI] mimr -v my M2 kirimi'llMz] m' mima- -w mg- M2 k22[mz][M2] mzmt' l ma Mi knlmz-llM1l "w 102ml' Theoretical considerations lead to the now generally ac? cepted copolymer composition equation which describes the ratio of the molar concentrations of two monomers in the initial copolymer formed from a given mixture of the monomers as follows:

dlMzlwlMs] TzlMzl'l-[Ml] ln this equation r1 equals len/k12 and r2 equals k22/k21. The terms r1 and r2 are called reactivity ratios. A very considerable body of experimental work has in general confirmed the copolymer composition equation.

A large proportion of possible pairs of monomers Vare incapable, because of their respective reactivity ratios, of forming under any conditions an instantaneous polymer having the same composition as the monomeric mixture from which it is formed. However there are certain monomer pairs which, in a proportion characteristic `of that pair, give a copolymer having the same composition as the particular monomeric mixture. In such instances, a batch polymerization can be carried out with a monomeric mixture of the particular composition. with a resultant homogeneous copolymer containing the same relative proportions off the monomers as in the initial monomeric reaction mixture. This composition is known as the polymerization azeotrope composition, and is rep resented by the equation:

[M2l [M1] T2-"1 Such an azeotrope composition can exist only for those monomer pairs wherein both r1 and r2 are less than one, or theoretically wherein both r1 and r2 are greater than one although no examples of the latter combination are known. .V While an understanding of interpolymerization involve ing only two monomers is now possible to a considerable extent, because of the development of the above-discussed theories, an increase in the number of monomers Patented Sept. 9, 1958 l Thus, taking a system involving two; monomers, M1 and M2, a growing polymer chain can ,acrylonitrile,-

to three or more obviously tremendously increases the possibilities and complications. Thus, for example if interpolymers of 100 monomers are to be considered, there are about 5000 possible monomer pairs, but about 160,000 different combinations of three monomers are possible, and'for each of these 160,000 combinations the variations in relative proportions of the three monomers are infinite. If the assumptions made in the development of the copolymer composition equation still hold true where three monomers are to be interpolymerized, it is apparent that the composition of the terpolymers formed at any given instance will now be dependent upon the rate of nine propagation steps which are dependent upon the relative concentrations of the monomers in the monomeric mixture and the reactivity ratio between each of the pairs of the monomers in the mixture. It has been pointed out that the study of terpolymers can be simplied somewhat by application of the copolymer composition equation, suitably modified for three-component systems, so as to eliminate from consideration monomers whoseability to interpolymerize is so slight that further investigation of such combinations is obviously not warranted. However, the discovery of terpolymers having particularly desired physical properties has to the present time been limited to the needle in the haystack type of investigation. There is an obvious need for some procedure in the terpolymer field whereby terpolymers of particular properties can be made with a reasonable degree of predictability.

In accordance with the present invention, we have found a group of terpolymers that can be made by freelradical-initiated batch polymerization and that have the very desirable property of clarity. These terpolymers are made by polymerizing a monomeric mixture of certain proportions of three monomers. The proportions giving clear terpolymers will vary from one monomeric mixture to another depending upon the particular monomers present in that mixture. The invention is particularly applied to monomeric mixtures consisting essentially of (a) a-methylstyrene, (b) acrylonitrile, (c) a monomer selected from the group consisting of methacrylonitrile, alkyl methacrylate. For example a monomeric mixture consisting of a-methylstyrene, acrylonitrile, and methacrylonitrile will, when subjected to free-radicalinitiated batch polymerization, give a clear terpolymer only if the relative proportions of a-methylstyrene, acrylonitrile, and methacrylonitrile are properly chosen in a manner to be hereinafter described. In contrast, a monomeric mixture consisting of a-methylstyrene, acrylonitrile, and methyl methacrylate will give a clear terpolymer on being subjected to free-radical-initiated batch polymerization only if the relative proportions of the three mentioned monomers in the monomeric mixture are within certain limits which in general are different from those of the aforementioned mixtures of a-methylstyrene, acrylonitrile, and methacrylonitrile and yet which are chosen in accordance with the same principle now to be discussed.

We have found that clear terpolymers of the nature described are made provided the proportions of three monomers in the monomeric mixture are chosen from the area lying along the line joining the binary polymerization azeotrope composition of a-methylstyrene and acrylonitrile on the one hand, and the binary polymerization azeotrope composition of oc-methylstyrene and the particular (c) on the other hand, as plotted on a triangularcoordinate graph. By way of example, taking the case where (c) is methacrylonitrile, the point of the binary azeotrope composition of -methylstyrene and acrylonitrile is placed along one side of a triangular coordinate graph at the proper location between the apex designating'y 100 percent a-methylstyrene and the apex designating 100 percent acrylonitrile. This point is 70 `weight percent a-methylstyrene and 30 weight percent On the, opposite side of the equilateral ,4 triangle, constituting the triangular coordinate graph, is placed the point representing the binary azeotrope composition of oc-methylstyrene and methacrylonitrile, this, of course, being located at the proper position on the side of the triangle between the apex representing percent a-methylstyrene and the apex representing 100 percent methacrylonitrile. This point is 56.6 weight percent a-methylstyrene and 43.4 weight percent methacrylonitrile. Now a straight line is drawn between these two points. This line cuts across the triangular coordinate graph, without touching the side of the triangle opposite the a-methylstyrene apex, which side represents varying proportions of acrylonitrile and methacrylonitrile in binary mixtures of same. Acrylonitrile and methacrylonitrile do not form a binary azeotrope. The said straight line joining the two points of binary azeotrope compositions describes three-component monomeric mixtures which, when subjected to free-radical-initiated batch polymerization, give clear terpolymers. Further, there is an appreciable area lying on each side of said line in which the terpolymers are essentially clear. However, one cannot go too far from this line without producing terpolymers which are not clear but range from hazy to opaque materials, or which, on the side of the line towards the a-methylstyrene apex, are low-conversion non-solid products. The inventionA particularly applies to the area lying within 5 percent on each side of said line; said 5 percent is measured on the graph in a direction normal to the line, and is equal to five one-hundredths of the shortest distance between an apex and the side of the triangle opposite the apex. (Another way of saying the same thing is that the invention particularly applies to the area of the graph bounded by two lines on opposite sides of and parallel to and 5 graphical units distant from said line.) Terpolymers made by polymerizing a monomeric mixture having a composition lying in the area within 5 percent on each side of the line joining the two binary polymerization azeotrope compositions, are generally clearer than polymers made from similar monomeric mixtures lying farther away from and on the same side of the line. In most systems all terpolymers made from monomeric mixtures having compositions in the area lying within 5 percent on each side of the line are clear. In some systems the area of clarity may not extend as far as 5 percent from the line. Those skilled in the art, having had the benet of the present disclosure, can easily determine by simple tests of the nature described herein which monomeric mixtures give clear terpolymers in a given polymerization system. In all events, the compositions of monomeric mixtures giving clear terpolymers will be found to constitute an area lying along and encompassing the line joining the two binary polymerization azeotrope compositions.

Because of the inability of a-methylstyrene to polymerize with itself under free-radical-initiated polymerization conditions, it is not practical to carry the polymerization to a high conversion with monomeric mixtures of the type described herein that contain high proportions of a-methylstyrene. Thus, monomeric mixtures whose compositions are more than about 5 percent away from the line joining the two binary polymerization azeotropes in the direction of increasing -methylstyrene content (i. e., lying between the line and the -methylstyrene apex and more than 5 percent away from the line), in general tend to give non-solid syrupy products even with extended polymerization times. Though such products be clear, they are not usually of practical interest. Therefore, the invention is particularly directed to polymers prepared from monomeric mixtures in which the proportions of the three monomers are within the area of clear terpolymers lying along the line joining the two binary azeotrope compositions but not more than about 5 percent (i. e., 5 graphical units) away from the line in the direction of increasing o-methylstyrene content.

The reasons for the clarity of terpolymer's made as defscribed are not known. The line joining the two binary azeotrope compositions does not represent what might be YCalled a series of three-component azeotropes. From Ymuch detailed data which we have obtained, the relative proportions of the three monomers in terpolymers made from monomeric mixtures lying along said line are not identical to the monomeric mixture from which the terpolymer is being prepared. In other words, during the course of a batch polymerization of a monomeric mixture whose composition is taken from the line, the composition of residual monomeric material drifts and the terpolymers `so formed are not homogeneous mixtures of polymer mol- -ecules all of which contain monomer units in the same ratio, but rather are mixtures of polymer molecules hav- ;ing varying proportions of the three monomer units therein. No heretofore known scientific facts or theories of interpolymerization explainour discovery. However, regardless of the various reasons for believing that terpolymers made from compositions lying along the line as aforesaid would be heterogeneous, and regardless of the actual reasons for the clarity of such terpolymers, it is apparent that the present invention makes possible the production of clear terpolymers with obvious attendant advantages, especially in iilms and molded articles made from the terpolymers.

The accompanying drawings are triangular coordinate graphs showing compositions of some three-component monomeric mixtures that give clear terpolymers on being subjected to free-radical-initiated batch polymerization.

Figure I represents the system ot-methylstyrene/acrylonitrile/methacrylonitrile Figure II represents the system ot-methylstyrene/acrylonitrile/methyl methacrylate.

By the present invention we can subject a given monomeric mixture consisting of three monomers, selected as described herein, to a batch polymerization and carry the polymerization reaction to complete or essentially complete, say 90 to 100 percent, conversion of all of the monomers and yet obtain a clear solid resinous terpolymer. (In some cases it is difficult to reach 90 percent conversion, but a solid product can still be obtained.) If desired, the polymerization can be stopped at any .point short of completion so long as polymerization conditions are such as to produce solid terpolymer, but this is not necessary in order to obtain a clear terpolymer and would seldom be advantageous. The higher the degree of conversion of monomeric mixtures, the greater the advantages of our invention. This is because the greatest extent of heterogeneity is found with complete conversion to polymers. A high conversion, i. e., at least 50 weight percent conversion and preferably at least 80 weight percent conversion, is preferred in practicing the invention. However,

Vsome of the benets of the invention may be realized even where the percentage conversion is as low as 20 percent. With very low conversions, the polymer formed tends to approach the perfect homogeneity existing in the first infinitely small increment of polymer formed. As pointed out above, commercial practicality requires that conversion be carried to a value more than a few percent, hence introducing the lack of homogeneity which up to now, the art has not known how to avoid other than by techniques such as gradual monomer addition. It is to be recognized that the extent of the area of clear terpolymers, lying along the line joining the two binary polymerization azeotrope compositions, is dependent not only on the particularv It is usually desirable that the three-component monomeric mixture contain at least 2 weight percent, and preferably at least 5 weight percent, of the monomer present in the smallest amount.

The invention is broadly applicable to any free-radicalinitiated interpolymerization of three-component monomeric mixtures containing the monomer combinations and in theproportions set forth herein, provided the polymerization is carried out by a batch procedure. By this it is meant that all of the monomeric materials to be employed are introduced simultaneously in the desired proportions into the polymerization reaction system. Ordinarily a single charge of monomeric materials will be placed in a reaction vessel and the single charge subjected to polymerization conditions until the polymerization is substantially complete. However, it is not outside the scope of our invention to introduce continuously a monomeric mixture containing the three monomers in fixed proportions into a flow-type polymerization stystem, whereby the initial polymerizable mixture passes away from its point of introduction and ultimately is recovered as polymer. 'Ihis can be accomplished by continuous flowing of the monomeric mixture into the first of a series of polymerization reaction vessels with continuous flow of reaction mixture from one vessel to another along a series of two or more such vessels with ultimate recovery of polymer from the last in the series. Those skilled in the art will understand that this operation is essentially a batch operation in the sense that additional monomeric material of composition different from the original mixture is not introduced into a partially polymerized material. Thus, the term batch polymerization, as used herein, means a polymerization which does not involve the gradual or incremental or subsequent addition of a monomer o-r monomers having a composition different from the initial monomeric mixture.

The invention is perhaps most advantageously effected by the mass or bulk polymerization procedure. In such procedure the reaction mixture is free from added solvent or other reaction medium and consists solely of monomers, resultant polymers, and catalyst and regulator, if any. An important advantage of the invention is that such a mass polymerization can be effected to produce a clear terpolymer in a situation in which it is impossible to use the gradual monomer addition technique discussed above.

lf desired, the interpolymers of the present invention can be made by the suspension or the emulsion polymerization techniques. For suspension polymerization a reaction medium such as water is used together with a small amount of suspending agent, for example tricalcium phosphate, carboxymethylcellulose, etc., to give a suspension of particles of initial monomeric mixture, which particles are not of such small size as to result in a permanently stable latex. Wherev the particles are of quite large size, this type of polymerization is often called pearl polymerization. To effect emulsion polymerization, snlcient amount of emulsifying agent, for example a water-soluble salt of a sulfonated long chain alkyl aromatic compound, a surface active condensation product of ethylene oxide with long chain aliphatic alcohols or mercaptans, etc., is employed along with vigorous agitation whereby an emulsion of the reactants in water is formed and the product is obtained in the form of a latex. The latex can then be coagulated if desired by known methods and the polymer separated from the water. For some applications the latex can be employed directly as for example for forming a lm, and the resulting 'lilm after evaporation of the water will be clear when the Ipolymers are made in accordance with the present invention. The emulsion technique has certain advantages particularly in that a very high degree conversion of the monomers is obtained with considerable rapidity, since the heat of reaction is easily carried oli" by indirect heat exchange with thereaction mixture which those skilled in the art. presence in the molecule of the group -NIN- bonded contains a considerable proportion Vof water. Such polymerizations are often effected with redox-type catalyst systems at Vmoderate temperatures of say 60 C. on down to C. and below.

The polymers of the present invention can also be made in the presence of an added organic solvent. lt should be recognized however that the presence of such a solvent ordinarily results in a polymer of lower molecular weight than that `obtained in the absence of the solvent.

Conventional recipes and procedures for effecting mass, solvent, suspension and emulsion polymerizations are so well-known to those .skilled in the art, that they need not be further detailed here.

From the foregoing, it will be apparent that the term. monomeric mixture, as used Vin the claims refers only to the polymerizable monomeric materials used in the process, and that additionally solvents, aqueous reaction media, catalysts, etc., `can be vpresent or not in the reaction mixture as may be desired in any particular case. In other words, in the claims monomeric mixture is not necessarily synonymous'with reaction mixture."

Polymerization can be effected by any of the wellknown free radical mechanisms. The polymerization is initiated and carried on by virtue of free radicals, which can be derived from the monomers themselves on simple heating of the monomeric mixture to a suitable temperature, or can be derived from `added free-radical-supplying catalysts, especially the per compounds and the azo compounds, or can be derived by'ultraviolet or other irradiation of the reaction mixture with or without the presence of photosensitizers, e. g., organic disultides. The examples set forth hereinafter describe therma polymerizations in which the polymerization reaction was initiated and maintained merely by heating the monomeric mixture in the absence of any added catalyst. In many instances it will be desired to add a suitable polymerization catalyst, in which case suflicient catalyst is employed to give a desired reaction rate. Suitable catalysts are of the free-radical-promoting type, principal among which are peroxide-type polymerization catalysts, and azo-type polymerization catalysts. Those skilled in the art are now fully familiar with a large number of peroxide-type polymerization catalysts and a suitable one can readily be chosen by simple trial. Such catalysts can be inorganic or organic, the latter having the general formula: ROOR", wherein R is an organic radical and R is an organic radical or hydrogen. These compounds are broadly termed peroxides, and in a more specific sense are hydroperoxides when R is hydrogen. R and R" can be hydrocarbon radicals or organic radicals substituted with a great variety of substituents. By way of example7 suitable peroxide-type catalysts include benzoyl peroxide, ditertiary butyl peroxide, tertiary butyl hydroperoxide, diacetyl peroxide, diethyl peroxycarbonate, 2- phenyl propane-Z-hydroperoxide (known also as cumene hydroperoxide) among the organic peroxides; hydrogen peroxide, potassium persulfate, perborates and other per compounds among the inorganic peroxides. The azo-type polymerization catalysts are also well-known to These are characterized by the to one or two organic radicals, preferably at least one of the bonds being to a tertiary carbon atom. By way of example of suitable azo-type catalysts can be mentioned Gr.06- azcdiisobutyronitrile, p bromobenzenediazonium lluoborate, N-nitroso-pbromoacetanilide, azomethane, phenyldiazonium halides, diazoaminobenzene, p-bromobenzenediazonium hydroxide, p-tolyldiazoaminobenzene The peroxy-type or azo-type polymerization catalyst is used in small but catalytic amounts, which are generally not in excess of one percent by weight based upon the monomeric material. A suitable quantity is often in the range of 0.05 to 0.5 .percent by weight.

Photopolymerization isanother suitable procedure for carrying yout the present invention. This is ordinarily accomplished by irradiating the reaction mixture with ultraviolet light. Any suitable source of light is employed having effective amounts of light with wave lengths of 2,000 to 4,000 Angstrom units. The vessel in which the polymerization is conducted should be transparent to light of the desired wave length so that the light can pass through the sides of the container. Suitable glasses are available commercially and include borosilicate (Pyrex), Vycor, and soft glass. Alternatively, the source of light can be placed directly over the surface of the monomer in a container or can be placed within the reaction mixture itself. In some instances it is helpful .to add a material that can be termed a. photosenstizer, i. e., a material .which increases the rate of photopolymerization, for example organic disuldes as described in U. S. Patent No. 2,460,105.

Choice of a suitable temperature for a given polymerization Will readily be made by those skilled in the art having been given the benefit of the present disclosure. In general, suitable temperatures will be found within the range of 0 C. to 200 C., although temperatures outside this range are not beyond the scope of the invention in its broadest aspects. The time required for complete polymerization will dependrnot only upon the temperature but also upon the catalyst if any is employed, the ability of the system to remove heat of polymerization, and the particular monomers employed. The examples set forth hereinafter give some illustrative information as to reaction times for particular polymerizations.

The term triangular coordinate graph as used herein is well understood. The accompanying figures are examples of such graphs and the use of same. However, for the sake of completeness the following statement can be made concerning the character of such triangular graphs. The graph is an equilateral triangle, divided off by three series of parallel lines each series being parallel to one side of the triangle. The distance between an apex of the triangle and the side opposite that apex represents variations in percentages of the component designated by that apex varying from percent to 0 percent in equal increments running from the apex to the opposite side of the triangle. For example, if the distance between the apex and the side of the triangle opposite the apex is divided into 100 equal parts by lines passing across the triangle and parallel to said side, each line represents l percent of the component for which that apex is designated. Thus, any point within the triangle represents a single three-component composition, the indicated percentages of the three -components totaling 100 percent.

As an aid in the choice of suitable proportions of monomers for polymerization in accordance with the invention the following data on reactivity ratios of certain monomer pairs are presented by way of example. The values given are considered the best ones represented in the literature or otherwise known (see Copolymers by Alfrey, Bohrer and Mark, Interscience Publishers, Inc., 1952, pp. 32-43). In many instances an attempt is made to set forth an approximate order of accuracy. These latter ligures, expressed as plus or minus certain values, should not however `be given too much credence since such attempts to evaluate possible errors are dependent to a considerable extent on subjective evaluation of the data. Most of the values for reactivity ratios given are for moderate temperatures, say between about room temperature (20 C.) and 100 C. Of course, the value of the reactivity ratios for a monomer pair is a function of temperature but the variation in reactivity ratios with temperature is quite small and is of little importance unless the polymerization is to be carried out at temperatures considerably removed from those mentioned. Likewise, the reactivity ratios given are for atmospheric or autogenous pressure. Only if the polymerization pressure is to be quite considerably increasedv will there be an important change in the value of the reactivity ratios. It may also be pointed out that in the case of highly watersoluble monomers the reactl 'vity ratio values may be shifted somewhat from those given, when polymerization is eected in an aqueous system. Those skilled in the art, having been given the benefit of the present disclosure, will be able to evaluate the effect, if any, of reaction conditions on the values given herein and determine the extent of such eifect. Similarly, those skilled in the art can determine by Well-known procedures the `correct reactivity ratios for monomer pairs not specilically set forth in the following tabulation, which tabulation is given by Way of example of some but not all of the monomers that are the subject matter of the present invention.

In the following tabulation each monomer in a pair is designated as M1 or M2. Substitution of the values for r1 and r2 in the equation given above for the binary polymerization azeotrope composition permits an immediate determination of the proper location for the two points to be placed on the triangular coordinate graph, between which points is drawn the line of clear terpolymers.

In the case of alkyl methacrylates other than methyl methacrylate, the reactivity ratios given above for amethylstyrene-methyl methacrylate can be used, on the assumption that they do not differ essentially for the purposes of this invention. This assumes that a moderate increase in the chain length of the alkyl group in the alkyl methacrylates over the single carbon atom in the methyl group of methyl methacrylate, or a branching of the chain if such is present, does not greatly alter the polarity and steric properties of the vinyl double bond. Anyone skilled in the art, desiring greater precision, can use well-known standard procedures to determine the reactivity ratios for a given binary system not previously reported in the art. With alkyl methacrylates having fairly long chain alkyl groups, the reactivity ratios tend to vdiffer considerably from those for the corresponding methyl methacrylate and hence should be individually determined. Whenever weight percent rather than mole percent is desired as a matter of convenience, mole percentages of the binary azeotrope compositions are easily converted to weight percent by use of the molecular weights of the particular M1 and M2. In the case of alkyl methacrylates, any of which can be Icopolyrnerized with -methylstyrene and acrylonitrile in the practice of this invention, special preference is given to the lower alkyl groups. Alkyl groups containing from l to 4 carbon atoms are particularly valuable, viz., methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, seo-butyl, tert.- butyl. However, the invention is also applicable to the alkyl methacrylates that contain alkyl groups of up to 8 carbon atoms per alkyl group and even higher.

The following examples illustrate some methods for practicing the present invention with respect to certain ternary mixtures of monomers. The general applicability of .the invention, `and advantages thereof, are shown in these examples. It will be appreciated that variations can be made in the particular choice of monomers, proportions, and methods of polymerization in accordance with the general teachings of the present specification, and the examples are not yto be taken as coextensive with the invention in its broadest aspects.

Example 1 This example concerns the ternary system at-methylstyrene/acrylonitrile/methacrylonitrile. The data obtained in this example are set forth graphically in liligure'V I of the drawings.

The composition of the t:methylstyrene/acrylonitrile binary azeotrope was calculated in the following manner according to the article by Mayo and Walling, Chemical Reviews 46, 199 (1950).

ot-Methylstyrene (M2) Acrylonitrile (M1) 1=0.06

86.3 grams mixture (60.3 100)/ 86.3:70 weight percent a-methylstyrene (26.0X)/86.3=30 weight percent acrylonitrile The foregoing calculations give the composition of the a-methylstyrene/acrylonitrile binary polymerization'azeotrope as 70 weight percent ot-methylstyrene, 30 Weight percent acrylonitrile.

By the same procedures, the binary polymerization azeotrope for a-methylstyrene/methacrylonitrile was calculated to be 56.6 weight percent a-methylstyrene, 43.4 weight percent methacrylonitrile.

A series of monomeric mixtures was made up, each mixture being prepared by admixture of the individual pure monomers in a Pyrex test `tube mm. long and having an internal diameter within the approximate range of 14 to 18 mm., usually about 16 mm. Each test tube containing the particular monomeric mixture was flushed with nitrogen in order to remove any air present in the gas space above the liquid, and the test tube was then sealed off at the top by heating the tube under nitrogen and pulling it out in the flame to seal the tube completely. Each particular monomer mixture was prepared and polymerized in duplicate.

After the various tubes containing the monomeric mixtures had been prepared, they were placed in a 90 C. constant temperature bath, and held there for 24 hours. At the end of that period they were moved to a 120 C. constant temperature batch and held there for 24 hours. At the end of this second 24-hour period the tubes were removed and placed in an oven maintained at C. andy held therein for 8 hours. An exception was samples 13 and 14 which were heated as follows: 48 hrs. at 90 C.; 621/2 hrs'. at 120 C.; 8 hours at 180 C.

The various monomeric compositions are set forth in detail in Table I. Table I designates each diiferent mixture by sample number. Sample No. 1 is near the binary ot-methylstyrene/acrylonitrile azeotrope composition. Sample No. 13 is the binary a-methylstyrene/methacrylo nitrile azeotrope composition. In Figure I a straight line has been drawn connecting the two binary azeotrope compositions when plotted on triangular coordinates.` The other samples were prepared with varying compositions so as to determine the clarity or lack of clarity of terpolymers made from a variety of monomer compositions both near the line and at a distance from the line on each side of the line.

At the end of the polymerization cycle described above, all the polymers formed in the sealed tubes were carefully examined visually by the same observer, looking through the diameter of the cylindrical body of polymer obtained by breaking and removing the glass tube; this cylinder of polymer conformed to the internal shape and size of the glass tube. These visual observations were checked by other observers. It was determined that the clarity noted for polymer samples is not significantly affected by variation in polymer cylinder diameter within the range of .about 14 to 18 millimeters. It is to be understood that where clarity of polymers is discussed herein, reference is made to the appearance on looking through a cylindrical body of the polymer having a diameter within the approximate range of 14 to 18 millimeters. The following words were adopted for describing the clarity of polymers.

C--Clear--es'sentially crystal clear H-Hazy--some cloudiness but slight T-Turbid-moderately cloudy O-Opaque-dense cloudiness-similar to milk glass in appearance Clear means relatively free from gross amounts of haze but allows the presence of slight haze to be detected with close examination in strong light. Specic notation that a sample was crysta clear means not only that no haze wasapparent tothe observer, but also that the sample showed .asparkling appearance Ias found in high quality crystal glassware.

The alcohol solubles content of many of the polymers was determined, using the following standard procedure:

A 0.3-gram-sample of polymer is dissolved in 20 ml. acetone (or other suitable solvent), then the polymer is precipitated by adding 250 ml. absolute ethanol to the solution; the precipitate is coagulated, filtered olf, dried and weighed. The average of two determinations is given.

The specic viscosity was determined on the undissolved residue from the alcohol solubles test. 'Ihe speciic viscosity determinations were made on a 0.1 weight percent solution of polymer in dimethylformamide.

TABLE I.-a-METHYLSTYRENE/ACRYLONI- of the line in the direction of'increasing a-methylstyrene content, while unacceptable point 8 is more than 5 percent from the line, in the same direction. The area of clear terpolymers in some regions extends beyond the percent line. Point 6 (a binary mixture) which is only about 3 percent from the line joining the two binary azeotropes, is turbid, so that the area of clear terpolymers along the line does not extend to the 5 percent line in this region. Note, however, point 5 which is also 3 percent away from the principal line and not far from point 6, yet which is clear.

The alcohol solubles content v(ASC) gives an approximate measure of the extent of conversion. The material soluble in alcohol is principally monomer; only very low molecular weight polymers, e. g., dimers and trimers, are soluble in alcohol. Thus, 100-ASC approximates the percentage conversion. It will be noted that the product obtained from the point 8 monomeric material had the highest ASC, and therefore the lowest conversion, of all the products tested in this manner. It is also interesting that the viscosity of the alcohol-insoluble residue of this material was lower than any of the others,v indicating lowest molecular weight.

In Figure I the dashed lines drawn parallel to the line joining the two binary azeotrope compositions are 5 percent on each side of the line, i. e., each is a distance from the line equal to 5 percentage points of composition as determined by dividing the distance between an apex and the center of the opposite side of the triangle into 100 equal equidistant parts; in other words, the two dashed lines are on opposite sides of and 5 graphical units distant from said line. In general terpolymers prepared from monomeric mixtures having compositions falling within the area within 5 percent of eachside of the line are clear.

TRILE/METHACRYLONITRILE TERPOLYMERS Composition, Alcohol Appearance Sample Weight, per- Solubles Specific Number cent Content, Viscosity aMS/ANIMN percent Clarity Color 69/31/0 11.65 0.061 Yellow. 67/28/5 13.00 0. 054 o. 62/18/20 17.00 0. 045 Deep yellow. 59/11/30 22. 48 0; 039 Do. 55/5/40 19. 50 0. O40 do Do. 53/0/47 i. T-Turbxd Orange. 70/20/10 25. 58 0. 042 CCle r Light yellow.

37.10 0.028 (3S-Clear (Syrup) Yellow. 60/5/35 27.30 0.056 C-Clear. Orange. 60/30/10 12.80 0. 074 O-Opaque D0. /30/20 10. 92 0. 055 w d0 D0. 50/10/40 15.19 0. 065 H-Hazy. D0. 56.6/0/43-4 C-Clear Deepyellow.

47/0/ H-Hazy Reddlsh orange.

aMS=a-Methylstyrene. AN Acrylonitrile. MN Methacrylonitrile.

Referring now to Figure I of the drawings, the clarity data given in Table I have been designated alongside each of the corresponding ternary monomeric mixture compositions indicated by a point on a triangular coordinate plot. The various numerals on Figure I located adjacent the respective points refer to the same number in Table I.

Examination of Figure I immediately shows that terpolymers prepared from monomeric mixtures having compositions within the area lying along the line joining the two binary azeotrope compositions were clear. Clear points 1-5 lie below but fairly near the line. Points 10--12 and 14 lying farther away from the line were opaque or hazy. On the opposite side of, but fairly near, the line, are clear points 7 and 9. Still farther away from the line is point 8, which although clear is not a good test of compatibility because the product was syrupy due to low conversion. Thus, the product of point 8 is not of the properties desired for this invention. It will be noted that. acceptable points 7 and 9 are Within 5 percent Example 2 This example presents data on the ternary system amethylstyrene/acrylonitrile/methyl methacrylate.

In the manner set forth in Example 1, the binary polyinerization azeotrope composition of a-methylstyrene/ methyl methacrylate was' calculated to be 40.7 weight percent -methylstyrene, 59.3 weight percent methyl methacrylate. As in Example l, the binary polymerization azeotrope composition for -methylstyrene/acrylonitrilc was calculated to be 70 weight percent a-methylstyrene, 30 weight percent acrylonitrile.

Samples containing varying proportions of the monomers were prepared and polymerized and observations made on the polymers in the manner described in Example l. These data are listed in Table Il and plotted in Figure II of the drawings. It will be seen that points l to 5, inclusive, 1S and 22, were on or approximatelyon the line joining the two binary azeotrope'compositions, that points 6 to 11, 14 and16 ranged from about 3 to about llper- 13 centage points away from the line and were scattered on both sides of the line, that points 12 and 13 were a farther distance from the line in the direction of increasing amethylstyrene content, while points 117-21, inclusive, were on the opposite side of the line and covered a wide variety of compositions.

The polymerization cycle used for points 1-11, 15 and 18 was 24 hours at 90 C., 24 hours at 120 C., 8 hours at 180 C.; that for points 16, 17, 19 and 20 was 24 hours at 90 C., 24 hours at 120 C.; that for points 12-114 and 21 was 24 hours at 90 C., l120 hours at 120 C.; that for point 22 was 24 hours at 90 C., 72 hours at 120 C., 8 hours at 180 C.

product. Point 9, about 3 percent away jfrorri the line, because of its lower conversion and viscosity is in general less desirable than the point 11 product even though closer to the line. This is readily attributable to the difterence in compositions as naturally a series of products a fixed distance from the line will differ markedly from each other since the relative proportions of the three monomers in the monomeric mixtures vary widely.

While the invention has been described herein with particular reference to various preferred embodiments thereof, and examples have been given of suitable proportions and conditions, it will be appreciated that variations from the details given vherein can be effected with- TABLE II. a METHYLSTYRNE/ACRYLONI- TRILE/METHYL METHACRYLATE TERPOLY- MERS Alcohol Composi- Solubles t1on, Wt. Specific Appearance Sample Number Percent AN/MS/ MMA Content Viscosity Clarity Color do C-Crystal Clear Colorless.

Do. Do. Light yellow.

Yellow. Colorlcss. Light yellow. Yellow. Colorless.

Do. D0.

Do. Yellow.

Do. Bluish White. White. Yellow. White.

Do. Colorless.

*No test for compatibility due to low conversion. AN=Acrylonitrile- MMA=Methyl Methacrylate.

The data of Table II, as plotted on Figure II, again show the clarity of terpolymers prepared from monomeric mixtures, whose composition is taken from the line joining the two binary polymerization azeotrope compositions and the area lying along the line. The area of clear terpolymers below the line, i. e., in the direction of decreasing oc-rnethylstyrene concentration, is rather extensive, points 6, 7 and 8 being clear. However, the area of clarity is limited, as shown by the fact that points 16-21 are hazy or opaque. As in the other figure, a dashed line has been drawn on each side of the line joining the two binary azeotrope compositions, at a distance of 5 percent from the line, setting forth a preferred area of monomer compositions for use in making terpolymers with these monomers.

Above the line, samples l2 and 13, which contained the greatest percentage -methylstyrene of the mixtures tested, resulted in syrupy products due to low conversion. Sample 10, about 8.5 percentage points above the principal line, also resulted in low conversion (about 50 percent) and the alcohol-insoluble portion had the lowest viscosity of all of the polymers obtained from points 1--11. After standing many months the product was still sufficiently soft to show slow cold How. It is thus seen that monomeric mixtures whose compositions lie more than about 5 percent above the principal line in the direction of increasing vt-methyistyrene content result in products less desirable than those obtained from mixtures having compositions lying within about 5 percent of the line. Sample l1, which for the purposes of the invention can be considered the equivalent of the composition nearest it which is on the 5 percent line, resulted in suiliciently high conversion and viscosity to give a satisfactory clear limited to those in the area ofxmixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of a-methylstyrener andacrylonitrile on the one hand and at-methylstyrener and the particular (c) on the other hand as plotted on an equilateral triangular coordinate graph, but not morethan 5 graphical units away from said line in the direction of increasing a-methylstyrene content.

2. A clear terpolymer prepared by free-radical-initiated batch mass polymerization of a monomeric mixture consisting of (a) a-methylstyrene, (b) acrylonitrile, and (c) a monomer selected from the group consisting of methacrylonitrile and alkyl methacrylates, the proportions of the three monomers in said monomeric mixture being limited to those in the Iarea of mixtures that produce clear terpolymers, said areaY encompassing the line joining the polymerization azeotrope composition of -methylstyrene and acrylonitrile on the one hand anda-methylstyrene and the particular (c) on the other vhand as plotted on an equilateral triangular coordinate graph, but not more 15 than graphical units away from said line in the direction of increasing a-methylstyrene content.

3. A clear terpolymer prepared by free-radical-initiated batch polymerization of a monomeric mixture consisting of (a) a-methylstyrene, (b) acrylonitrile, and (c) methacrylonitrile, the proportions of the three monomers in said monomeric mixture being limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of ct-methylstyrene and acrylonitrile on the one hand and a-methylstyrene and methacrylonitrile on the other hand as plotted on an equilateral triangular coordinate graph, b ut not more, than 5 graphical units away from said line in the direction of increasing a-methylstyrene content.

4. A clear terpolymer prepared by free-radical-initiated batch polymerization of a monomeric mixture consisting of (a) a-methylstyrene, (b) acrylonitrile, and (c) an alkyl methacrylate, the proportions of the three monomers in said monomeric mixture being limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of a-methylstyrene and acrylonitrile on the one hand and a-methylstyrene and said alkyl methacrylate on the other hand as plotted on an equilateral triangular coordinate graph, but not Vmore than 5 graphical units away from said line in the direction of increasing a-methylstyrene content.

5. A clear terpolymer prepared by free-radical-initiated batch mass polymerization of a monomeric mixture consisting of (a) wmethylstyrene, (b) acrylonitrile, and (c) a lower alkyl methacrylate, the proportions of the three monomers in said monomeric mixture being limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of a-methylstyrene and acrylonitrile on the one hand and a-methylstyrene and said lower alkyl methacrylate `on the other hand as plotted on an equilateral triangular coordinate graph, ibut not more than 5 graphical units away from said line in the direction of increasing a-methylstyrene content.

6. A clear terpolymer prepared by free-radical-initiated batch polymerization of a monomeric mixture consisting of (a) a.methylstyrene, (b) acrylonitrile, and (c) methyl methacrylate, the proportions of the three monomers in said monomeric mixture being limited to those in the area of mixtures that pro'duce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of a-methylstyrene and acrylonitrile on the one hand and u-methylstyrene and methyl methacrylate on the other hand as plotted on an equilateral triangular coordinate graph, but not more than 5 graphical units away from said line in the direction of increasing a-methylstyrene content.

7. A clear terpolymer prepared by free-radical-initiated batch polymerization, to a conversion sufficiently high to give a solid product,`of a monomeric mixture consisting of (a) a-methylstyrene, (b) acrylonitrile, and (c) a monomer selected from the group consisting of methacrylonitrile and alkyl methacrylates, the proportions of the three monomers in said monomeric mixture being limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of a-methylstyrene and acrylonitrile on the one hand and a-methylstyrene and the particular (c) on the other hand as plotted on an equilateral triangular coordinate graph, but not more than 5 graphical units away from said line in the direction of increasing a-methylstyrene content.

8. A polymerization process which comprises forming a three-component monomeric mixture consisting of (a) a-methylstyrene, (b) acrylonitrile, and (c) a monomer selected from the group consisting of methacrylonitrile and alkyl methacrylates, the proportions of the three monomers in said monomeric mixture being limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of a-methylstyrene and acrylonitrile on the one hand and a-methylstyrenc and the particular (c) on the other hand as plotted on an equilateral triangular coordinate graph, but not more than 5 graphical units away from said line in the direction of increasing a-methylstyrene content, and subjecting a batch of said monomeric mixture to free-radicalinitiated batch polymerization forming an essentially clear homogeneous high molecular weight terpolymer.

9. A polymerization process which comprises forming a three-component monomeric mixture consisting of (a) a-methylstyrene, (b) acrylonitrile, and (c) a monomer selected from the group consisting of methacrylonitrile and alkylmethacrylates, the proportions of the three monomers in said monomeric mixture being limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of -methylstyrene and acrylonitrile on the one hand and a-methylstyrene and the particular (c) on the other hand as plotted on an equilateral triangular coordinategraph, but not more than 5 graphical units :away 'from said line in the direction of increasing o-methylstyrene content, and subjecting a batch of said monomeric mixture to free-radical-initiated batch mass polymerization forming an essentially clear homogeneous high molecular weight terpolymer.

10. A process according to claim 8 wherein (c) is methacrylonitrile.

11. A process according to claim 8 wherein (c) is a lower alkyl methacrylate.

12. A process according to claim 8 wherein (c) is methyl methacrylate.

, 13. A clear terpolymer prepared by free-radical-initiated batch polymerization of a monomeric mixture consisting of (a) a-methylstyrene, (b) acrylonitrile, and (c) a monomer selected from the group consisting of methacrylonitrile and alkyl methacrylates, the proportions of the three monomers in said monomeric mixture being limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of a-methylstyrene and acrylonitrile on the one hand and a-methylstyrene and the particular (c) on the other hand as plotted on an equilateral triangular coordinate graph, with the further limitation that said proportions of the three monomers are restricted to the area ofsaid graph bounded by two lines on opposite sides of and parallel to and 5 graphical units distant from said line.

14. A 4clear terpolymer prepared by ree-radical-initiated batch polymerization of a monomeric mixture consisting of (a) a-methylstyrene, (b) acrylonitrile, and (c) a monomer selected from the group consisting of methacrylonitrile and alkyl methacrylates, the proportions of the three monomers in said monomeric mixture being designated by the line joining the polymerization azeotrope composition of nt-methylstyrene and acrylonitrile on the one hand and a-methylstyrene and the particular (c) on the other hand as plotted on an equilateral triangular coordinate graph.

15. A terpolymer according to claim 13 wherein (c) is methacrylonitrile.

16. A terpolymer according to claim 13 wherein (c) is an alkyl methacrylate.

17. A terpolymer according to claim 13 wherein (c) is methyl methacrylate.

References Cited in the tile of this patent UNITED STATES PATENTS 

1. A CLEAR TERPOLYMER PREPARED BY FREE-RADICAL-INTITIATED BATCH POLYMERIZATION OF A MONOMERIC MIXTURE CONSISTING OF (A) A-METHYLSTYRENE, (B) ACRLONITRILE, AND (C) A MONOMER SELECTED FROM THE GROUP CONSISTING OF METHACRYLONTRILE AND ALKYL METHACRYLATES, THE PROPORTION OF THE THREE MONOMERS IN SAID MONOMERIC MIXTURE BEING LIMITED OT THOSE IN THE AREA OF MIXTURES THAT PRODUCE CLEAR TERPOLYMERS, SAID AREA ENCOMPASSING THE LINE JOINING THE POLYMERIZATION AZEOTROPE COMPOSITION OF A-METHYLSTYRENE AND ACRYLONTRILE ON THE ONE HAND AND A-METHYLSTYRENE AND THE PARTICULAR (C) ON THE OTHER HAND AS PLOTTES ON AN EQUILATERAL TRINGULAR COORDIANTE GRAPH, BUT NOT MORE THAN 5 GRAPHICAL UNITS AWAY FROM SAI LINE IN THE DIRECTION OF INCREASING A-METHYLSTYRENE CONTENT. 